Rheostat



March 3, 1964 R. VRADENBURGH 3,123,796

RHEOSTAT Filed Nov. 24, 1961 4 Sheets-Sheet 2 AW w foeegr Mpqoavawgcy March 3, 1954 R. VRADENBURGH 3,123,796

RHEOSTAT Filed Nov. 24, 1961 4 Sheets-Sheet s March is, 1964 R. VRADENBURGH 3,123,796

RHEOSTAT Filed NOV. 24, 1961 4 Sheets-Sheet 4 INVENTOR. 564 VPAOEIYBUQGH United States Patent 3,123,796 RHEOSTAT Robert Vradenburgh, Yonkers, N.Y., assignor to Ward Leonard Electric Co., Mount Vernon, N,Y., a corporation of New York Filed Nov. 24, 1961, Ser. No. 154,584 12 Claims. (Cl. 338-174) This invention relates to electrical ring type rheostats and is directed particularly to the rotatable mounting means supporting the sliding contact brush and to the stop means for limiting the arc of travel of the sliding contact brush.

In one form of the present ring rheostats, the rotatable mounting means has a resilient member for supporting the main sliding contact brush and an extension of this member for placing the shaft of the rotatable mounting means under pressure to take up the end play and apply pressure to a collector ring or second contact brush. In other forms a separate helical spring is employed for this purpose. The resilient member may be a berylliumcopper contact spring made from a complicated die. The manufacture of these spring members is further complicated by variations in temper, hardness and thickness, which affect the final shape and pressures developed. In order to insure uniformity of contact pressure, the spring member should be clamped in a form and heat treated.

Also in present ring rheostats, the porcelain drive head supporting the resilient member is mounted on and keyed with a metal drive shaft. The are of travel of the porcelain head and shaft is determined by stop means formed by projections on the porcelain head and base. Excessive torque applied through the shaft can break these projections which are inherently weak structurally. It is desirable to provide a sturdier and inexpensive means of limiting the are of travel.

An object of the invention is to provide an improved ring type rheostat with 'a simplified inexpensive resilient means for supporting the main sliding contact brush, eliminating end play and applying pressures to a collector ring or second contact brush.

Another object of the invention is to provide a ring ty'pe rheostat with sturdy means for limiting the arc of rotation of the sliding contact brush.

Another object of the invention is to provide a ring type rheostat of high performance characteristics that is made of fewer and simpler parts that are inexpensive to manufacture and assemble.

Other and further objects and advantages will be apparent from the following description taken in connection with the drawings, in which:

FIG. 1 is a top view of the rheostat;

FIG. 2 is a sectional view taken along lines 2-2 of FIG. 1;

FIG. 3 is a bottom view of the rheostat;

FIG. 4 is a sectional view taken along lines 44 of FIG. 2;

FIG. 5 is a sectional view taken along lines 5-5 of FIG. 2;

FIG. 6 is a sectional view of the bushing, shaft and spring taken along lines 66 of FIG. 2;

FIG. 7 is a top view of the base;

FIG. 8 is an exploded perspective view of the rheostat illustrated in FIG. 2

FIG. 9 illustrates another embodiment of the rheostat with the view taken along the same section as FIG. 2;

FIG. 10 is a sectional view taken along lines 1(l-1tl of FIG. 9;

FIG. I1 is a top view of another embodiment of the rheostat;

FIG. 12 is a sectional view taken along lines 12--12 of FIG. 11;

FIG. 13 is a sectional view taken along lines 1313 of FIG. "12;

FIG. 14 is a fragmentary side view of the drive head; and

FIG. 15 illustrates a modified form of the spring.

Referring to FIGS. 2 and 8, a rheostat is illustrated comprising a ring-shaped resistor 20, a ceramic base 21, and a drive member 23 rotatably mounted in the ceramic base to support the contact brush 22 in sliding engagement with the resistor. Stop means 24 is provided on the base and drive means to limit the arc of movement of the contact brush 22.

Referring to the embodiment illustrated in FIGS. 1 to 4, the base 21 is preferably formed as a single piece and comprises a circular disc portion 25 with a central opening 26, a circular flange 27, and a terminal supporting block 28. The flange portion 27 is spaced from the peripheral edge of the disc portion 25. This provides a flat, radial seating surface 29 for the resistor 20. The ring-shaped resistor 20 rests on this surface and is fastened thereto in any Well-known manner. The resistor 20 extends over an are A (FIG. 4-) and has terminals 30 and 31 at each end thereof to provide attachment of electrical leads. As best illustrated in FIG. 7, the block 28 extends from the flange 27 to the edge of the disc portion 25 and is located bet-ween the ends of the resistor 20. On the opposite side of the disc portion 25 are four bosses '32 with slots 33 for receiving the index 56 depending on the desired position of the rheostat.

A metal collector ring 34 has a circular portion of the same diameter as the flange 27 sitting on the flat surface 35 (FIG. 7) of the flange portion 27 and a radial terminal portion. A notch 36 is provided to index the collector ring in cooperation with the projection 40 extending from the ring 34 (FIGS. 2 and 7). The collector ring is fastened to the block 28 by means of a rivet 41 passing through the terminal portion and the block. Passage is provided through the block 28 for the rivet and the ends of the rivet are turned to secure the rivet and the collector ring to the base.

The flange 27 forms a recess 44 concentric to the opening 26 and has an inner sloped conical shaped wall 45 with longitudinally extending grooves 46. A washer 47 with outer peripheral projections 48 fits into the recess 44 with the projections 48 keyed into the slots 46 to prevent rotation of the washer (FIG. 4). At the inner edge, forming the hole through the washer, a projection 49 extends normal to the washer and away from the disc portion to form an are limiting stop (FIG. 2). The Washer is made, preferably, of metal. The drive means generally comprises a cylindrical shaft 50, a drive head or bushing 51 and a resilient brush supporting member 70. The drive means is rotatably mounted in the thread sleeve 52 which fits in the opening 26 of the base 21. The sleeve has a hexagonal-shaped flange 53 fitting in a hexagonal-shaped recess 54 (FIG. 7) in the base 21 to prevent rotation of the sleeve 52 and in cooperation with the nut 55 to secure the sleeve to the base. An index 56 and washer 57 are held between the nut 55 and the bottom surface of the base 21. The index 56 fits in the slot 33 between the bosses 32 on the base 21 (FIG. 3). The shaft 50 is rotatably fitted in the sleeve 52 and held in a substantially fixed longitudinal relation with the sleeve 52 by a retaining ring 58 fitting in a groove 59 in the shaft and by the projection 69 extending radially from the side of the shaft. The projection 60 cooperates with the fixed projection 49 to form a stop means limiting the arc of rotation of the shaft 50.

The cylindrically shaped drive head or bushing 51 has a cylindrical bore 51a with two radially and longitudinally extending grooves 61 and 62 which extend substantially the entire length of the bushing. The bushing slides on the shaft with the projections 63 and 6t fitting in the grooves 61 and 62 to key the shaft 519 and the bushing 51 together for rotational movement while permitting relative longitudinal movement between the shaft 51 and the bushing 51. The shaft 51) has a flange 64 which fits in recess 65 in the bushing to seat against the shoulders 66. Tiis interlocking retains the bushing on the end of the s aft.

The bushing 51 has a radially extending flange 67 on the outer end. The inner radial surface of the flange 57 is sloped at an angle to the axis of the shaft 51) and has grooves 68 and 69 on opposite sides of the longitudinally extending portion. The outer surface of the longitudinally extending portion has two concave surfaces reducing the diameter of the bushing to permit closer positioning of the grooves 68 and 69 to the axis of the shaft 50. The bushing is preferably made of a non-conductor, such as ceramic.

The resilient brush support member '70 is a single piece of steel spring wire which may be alsoPhosphor bronze, music wire, stainless steel and various nickel alloys. The spring is formed by automatic machinery and has two lower legs 73, 74 and two upper legs 75, 76 connected by the intermediate pieces 77, 7% (FIG. 8) with curved ends to form S-shaped members or portions. The lower legs 73, 74 are spaced and the upper legs 75, '76 are connected at one end of the looped member 72. The looped member 72 has three straight sides for receiving the rectangular block mounting portion 72a of the graphite composition brush 21-. The legs 73 and 74- are secured to the collector washer 71 by seating the legs underneath the projections 8t and 81 on the collector washer, as illustrated in FIG. 5. Thus, the spring 71! and the washer 71 rotate about the axis of the shaft 511 as a unitary piece. The pigtail braided wire 32 is attached to the mounting block 72a on the brush 22 or brazed or soldered to the collector washer 71 to conduct electricity from the collector washer to the brush. The sliding contact member or brush Z2 is molded and is made of metallic and graphite particles for self-lubrication. The Spring 71 is compressed and slides around the mounted bushing 51 with the legs 73 and 74 sliding under the projections 80 and 81. Upon release, the spring presses against the flange 67 to' force the bushing against the shaft flange 64- which, in turn, presses the retaining ring 58 against the sleeve 52. The spring 71) also presses the collector washer 71 against the collector ring 34 to produce a firm electrical contact therein for electrical transference. The shaft 56 has a longitudinally extending flat surface 83 for receiving a control knob or other rotating devices (not shown) to turn the shaft 59 and thus the brush 22. As best illustrated in FIG. 1, the resistor 21) extends over an arc A. The stop means formed by the projections 69 and 49 limits the path of travel of the arc crush 22 to this arc.

A particular feature of this rheostat is the sturdy construction of the stop means. The stop member is made of steel or other suitable material. The projections bear against the walls of the slots 46. In this embodiment, projections and four slots are provided to transmit the impact of the projections against the projection 49 to prevent localizing of the force of impact at any single point. The shaft 5% is also preferably made of metal, as well as the projection 6%). Further, the projections seat in recesses which have a substantial circumferential dimension to prevent the breaking or crushing of the base 21.

As illustrated in FIG. 4, the projection 49 extends over an arc B to limit the path of movement of the brush 22 to-the are A. On assembling the spring 70 on the bushing or drive head 51, the normally straight lower legs 73, '74 of the spring 713 are flexed inwardly to engage the concave sides 51a of the drive head 51 to assume a concave configuration, as illustrated in FIG. 1. The legs 73, 74 are held in this position by the ears or projections 80, 31

on the washer 71. The washer has a rectangular opening 84 in which the bushing 51 fits. The cars 80, 81 are formed midway in the side edges of the opening by stamping and bending strips from the washer. The legs partially lit in the space formed by the ears to hold the le s in the concave position. The spring and drive head form a unitary structure rotating about the axis of the shaft 51 This type of engagement of the spring with the concave portions of the drive head eliminates all backlash and the drive head rotates the spring member without lost motion. 7

The spring 71} is thus held in a fixed transverse relationship with respect to the drive head by means of the curved portions 85, 36 engaging the bushing curved or convexed surface 87 and by the legs 73 and 74 fitting in against the concave portions and the ends 88 and 89 engaging the bushing curved portion 911, which is opposite to the curved portion 87 (FIGS. 1 and 8). The portions 85, 36 prevent or limit the inward movement of the spring and brush 22 toward the center of the shaft 59 and the concave legs '73, 74 and the ends 88 and 89 prevent or limit the outward movement of the brush 22 away from the center of the shaft Thus, the brush 22 is radially positioned so as to always contact the resistor 20.

In the flange 67, V-shaped groove 67a, 1) are provided on the underside. The grooves are sloped at an angle to a plane normal to the axis of the shaft 5:? and parallel to the plane through the center of the shaft 50 and the brush 2 2. The grooves have their lower portion on the side of the axis, opposite to that of the brush 22. The legs 75 and '76 engage these grooves on the side of the shaft opposite to the brush 22.. The spring pressure applied by the brush 22 against the resistor 26 may be adjusted by the relationship of the diameter of the spring 7 fl and the sides of the V-shaped grooves. The V-shaped grooves are deeper at the end adjacent to the brush 22 and gradually taper toward the opposite end of the flange. The back ends of the grooves are, therefore, shallower than the front ends and permit the spring to flex within the region between the brush end and the point of contact of the spring and flange. The location of the contact end of the groove may be changed by molding techniques to increase or decrease contact pressure. Thus in addition to changing the size of the wire of the spring, the grooves may be also changed to vary the pressure relationship between the brush and winding and between the collector washer and the collector ring. The contact between the legs 75 and 76- may occur at any point along the grooves. The preferred position would coincide with the center line of the drive head.

A modification of the flange and fulcrum is illustrated in FIGS. 11-14. In FIG. 15 a modification of the spring is illustrated in which the point of engagement of the spring against the flange is attained by providing projections on the upper legs 75, 76. The V-shaped grooves have a uniform depth and the projections fit in the grooves to form the fulcrum point.

In FlGS. 9 and 10 another embodiment of the invention is illustrated. The resistor 20, the collector ring 34 and the spring 70, the collector washer 71, sleeve 52, nut 55, indexing means 56, washer 57 and retaining ring 58 are identical to the corresponding members in the previously described embodiment, illustrated in FIG. 2.

The base 161 is the same as the base 21 except the conical surface 45 does not have the grooves 46. Instead, a projection 1&6 extending over an arc C is formed on the surface 45 of the base and extends toward the center of the base 101. The projection 106 cooperates with the projection 111} on the ring member 111 to form a stop means for limiting the arc of rotation of the shaft 1112. The shaft 102 is similar to the shaft 51) except that, instead of having projections 6% and 63, the shaft has a square portion 1133 with the sides of the square equal to the diameter of the shaft 102. The bushing 114 has a square bore 115 extending through the entire length of the bushing. The diameter of the shaft is approximately equal to the length of the side of the bore to support the bushing along the shaft. The square portion 103 in addition to supporting the bushing keys it to the shaft. The corners of the square section overlap with the flange 53 of the sleeve 52 to longitudinally restrict the shaft with the sleeve in cooperation with the retaining ring 58. The ring 111 is keyed to the shaft 102 by having a rectangular hole corresponding to the rectangular portion 193. In the embodiment illustrated, the hole and portion 103 are square. The ring member 111 and projection 110 rotate with the shaft with the projection engaging the stop 106 to limit the arc of travel.

In FIGS. 11-l4, another embodiment of the invention is illustrated in which the resistor member 20 and the brush 22 and the spring member 70' are the same as in the previous embodiment. The collector ring 120 is modified by providing ears 121 and 122 on each side of the tab 123 to act as stops for engagement by the projection 124 on the collector washer 125. This provides a metal type of stop with the stops located at the greatest possible distance from the center line of the metal shaft 126. The stops 121 and 122 are spaced from the other parts of the rheostat and, thus, do not require as high stringent tolerances as in the previous embodiments. Thus a dual advantage is secured by having these stops with a greater capacity to absorb shock and which are spaced so as not to interfere with the operation of other parts of the rheostat or require fine dimensioning of the parts. The collector ring may be fastened in a similar manner to the base 128 as the collector ring of the other embodiments. Since the stops are mounted on the collector ring, the base has been modified to eliminate projections and grooves in the recess of the base. Otherwise the base is similar to the bases of the previous embodiments. These modifications provide for a simpler molding of this member.

The spring member 70 is similar to the spring members of the other embodiments. However, an additional member has been provided comprising a metal contact arm 139, which fits over the flange 131 of the modified contact head 132. The flange 131 is preferably uniform in thickness and has a flat undersurface 133. The metal contact arm engages the surface and has raised portions 134 which are positioned on the opposite side of the center line of the shaft 126 from the contact brush 22. The upper legs 75 and 76 of the spring engage these raised portions to provide a fulcrum for applying pressure to the contact brush. The metal contact arm has a generally rectangular shaped slot 135 for fitting over the brush 22 and is resilient to respond to the resiliency of the spring 70. The arm protects and covers the spring. The drive head or bushing 132 and the shaft 126 have been modified by providing keys 137 at the upper end of the shaft to fit in slots or grooves 138 in the drive head and thus interlock the drive head or shaft so that the shaft will rotate the head and drive the spring 70 and brush 22.

The location of the fulcrum point between the spring member and the drive member may be easily changed in the fabrication of these parts. In the embodiment of FIG. 2 the spring wire size may be changed to vary the depth the wire seats in the V-shaped grooves. In the embodiment of FIG. 15, the notches may be located at the desired point of the upper legs. The grooves 134 of the embodiment of HG. 12 may be positioned at various distances from the brush 22.

The foregoing rheostats have many advantageous features over prior rheostats. The stop means in each of the embodiments are sturdier than the stop means of prior rheostats. The rotating portion of the stop means may be a metal piece keyed to the metal drive shaft or a metal projection as part of the metal drive shaft. The fixed portion of the stop means may be either a ceramic projection or a projection and metal piece fixedly fastened to the base. The impact against the ceramic base is distributed either through a multiple of contacting points, as in the embodiment of FIG. 2, or by a broad stop, as in the embodiment of FIG. 9. In the embodiment of FIG. 12 the force is applied through the rivet attaching the collector ring to the base. In each of these instances the point of transmission of the rotative force applied by the drive shaft is spaced radially from the axis of the drive shaft so as to reduce the leverage. This is particularly the case with the upstanding ears of the embodiment of FIG. 12. The cars are located at the greatest possible distance from the drive shaft axis or center line permitting less stringent tolerances on the stop portions and their location.

The spring member 7i) and drive bushing 51 provide a more flexible combination in adaption to difierent requirements and a greater ease in manufacture. The spring member is relatively inexpensive to make. No expensive forms for heat treatment are required and a variety of standard spring wire material may be used depending on the operating temperatures involved. Further, a more uniform product is attained without the need for special treatment since the wires are drawn to a uniform gage size.

in addition to the above flexibility of design and simplicity of manufacture, the parts are easily assembled.

Various modifications may be made in the described embodiments and the arrangement of the spring member and bushing flange applied to other forms of the rheostat within the spirit and scope of the invention as set forth in the appended claims.

I claim:

1. A rheostat comprising a base with a peripheral edge, a circular flange spaced radially inward from the peripheral edge to form a seating surface, a terminal block extending from the flange to the peripheral edge; a ring type resistor extending over an arc of less than 360 and having ends adjacent the terminal block; a collector ring mounted on and fastened to said flange for receiving voltages tapped from said resistor; drive shaft rotatably mounted on said base with a drive head having a lateral flange; a single piece resilient member mounted on said drive head between said lateral flange and said collector ring to snugly press said shaft on said base and support a siiding contact for rotation through the arc of the resistor; said drive shaft having two keys on opposite sides thereof with one key longer than the other; said drive head having longitudinally and radially extending slots for receiving said keys; a metal stop member concentric with the shaft and having a longitudinally extending stop projection and lateral peripheral projections; said flange having notches facing said shaft and said projections fitting in said notches to prevent rotation of said metal stop member; said longitudinally extending projection overlapping with said long key to form a stop means limiting the arc of travel of the sliding contact to the arc of the resistor.

2. A rheostat comprising a base with a peripheral edge, a circular flange spaced radially inward from the peripheral edge to form a seating surface, a terminal block extending from the flange to the peripheral edge; a ring type resistor extending over an arc of less than 360 and having ends adjacent the terminal block; a collector ring mounted on and fastened to said flange for receiving voltages tapped from said resistor; drive shaft rotatably mounted on said base with a drive head having a lateral flange; a single piece resilient member mounted on said drive head between said lateral flange and said collector ring to snugly press said shaft on said base and support a sliding contact for rotation through the arc of the resistor; said drive shaft having an intermediate rectangular portion; said drive head having a rectangular shaped bore overlapping said rectangular portion to key said shaft to said head; a metal washer having a rectangular center opening and a radially extending projection; said Washer mounted on said shaft at the rectangular portion to rotate with the shaft to prevent rotation of said shaft; said disc flange having an inwardly extending block for engagement by said projection to form a stop means limiting the arc of travel to the arc of the resistor.

3. A rheostat comprising a base with a peripheral edge, a circular flange spaced radially inward from the peripheral edge to form a seating surface, a terminal block extending from the flange to the peripheral edge; a ring type resistor extending over an arc of less than 360 and having ends adjacent the terminal block; a collector ring mounted on and fastened to said flange for receiving voltages tapped from said resistor; drive shaft rotatably mounted on said base with a drive head having a lateral flange; a single piece resilient member mounted on said drive head between said lateral flange and said collector ring to snugly press said shaft on said base and support a sliding contact for rotation through the arc of the resistor; said drive shaft having two keys at one end; said drive head having a bore for receiving said shaft and two longitudinally extending slots for said keys to interlock the drive shaft and drive head; a collector washer between said resilient member and said collector ring for slideably engaging said collector ring; said collector ring having two projections on opposite sides of said terminal and a projection on said washer to engage said projections to limit the arc of travel of the sliding contact.

4. A ring type rheostat comprising a disc-shaped base having a central opening, a flange concentric to the opening and spaced from the peripheral edge of the base to form a seating surface and a terminal block extending from the flange to the peripheral edge; a ring type resistor extending over an arc of less than 360 and having ends adjacent the terminal block; a collector ring mounted on said flange and having a radial terminal fastened to said block to secure the ring to the flange; drive means rotatably mounted on said base and having a drive shaft extending through said opening, a drive head with a lateral flange and a spring member with a collector washer mounted between said flange and said collector ring, said spring member being formed from spring wire and having two S-shaped portions with upper legs connected by a brush supporting arm and with lower legs connected to said collector washer; said collector washer having a rectangular opening for receiving said drive head and raised notches for pressing said lower legs against said drive head to rotate said spring member and said brush, said spring member bearing said washer against said collector ring and against said flange to provide a fulcrum between said upper legs and flange for applying brush pressure against said resistor and to take up longitudinal movement between the drive means and the base.

5. A rheostat comprising a base with a central opening and a ring resistor and collector ring concentric thereto, rota-table drive means extending through said opening and having a lateral flange spaced from said collector ring, a resilient member with a collector washer, said resilient member extending longitudinally tosaid drive means and positioned between said flange and said collector washer to press said collector washer into rotatable engagement with said collector ring in current transfer relation, said resilient member formed from a single piece of spring wire With two S-shaped portions extending longitudinally and positioned on opposite sides of the drive means and with a sliding contact supporting arm connecting the two portions and engaging said ring resistor, said drive means having flattened opposite sides, said collector washer forcing the lower portions of said S-shaped portions against said flattened sides to form a gripping means between said resilient member and said drive means for rotation of said resilient member and said collector washer with said drive means.

6. A rheosta-t as set forth in claim wherein each of said S-shaped portions has upper legs and lower legs and said lateral flange has means for forming a fulcrum engagement of said upper legs against said flange to render said upper legs and said sliding contact supporting arm resilient for applying pressure of said sliding contact against said resistor.

7. In a rheostat having a base with a circular resistor engaged by a sliding contact and a collector ring engaged by a rotatable collector washer, a sliding contact supporting means mounted on said base and comprising a drive head having a lateral flange and a resilient member having two resilient arms positioned between said flange and said collector washer and extending longitudinally on opposite sides of said drive head and supporting a sliding contact engaging said resistor, and said lateral flange having a fulcrum means for engaging said resilient arms to resiliently press said sliding contact in engagement with said resistor.

8. In a rheostat having a base with a circular resistor engageable by a sliding contact and a drive means rotatably mounted on said base, the combination of a drive head having a lateral flange and two spring wire arms extending longitudinal to said drive means and mounted on opposite sides of said drive head and supporting a sliding contact engaging said resistor, said lateral flange having means for engaging each of said arms at a fulcrum point to resiliently press said sliding con- ;tact in engagement with said resistor.

9. in a rheostat having a base with a circular resistor engaged by a sliding contact and with a collector ring for receiving voltages from said contact, a drive means rotatably mounted on said base, the combination of a drive head having a lateral flange, a single piece of spring wire for supporting a sliding contact and a collector washer for slidably engaging the collector ring, said drive head secured to said drive means for rotation thereby said spring wire having two S-shaped portions positioned on opposite sides of the drive head and generally longitudinal thereto each with an upper and lower arm, said upper arms connected by a sliding contact support and said lower arms pressed by said collector washer against said sides to rotatably lock said spring wire to said drive head and said lateral flange having a surface at an angle to the axis of the drive head and V-shaped grooves for receiving the upper arms to form fulcrum points for resiliently pressing the sliding contact against the resister.

10. In a rheostat having a base with a circular resistor engaged by a sliding contact and with a collector ring 7 for receiving voltages from said contact, a drive means rotatably mounted on said base, the combination of a drive head having a lateral flange, a single piece of spring wire for supporting a sliding contact and a collector washer for slideably engaging the collector ring, said drive head secured to said drive means for rotation thereby, said spring wire having two S-shaped portions positioned on opposite sides of the drive head and generally longitudinal thereto each with an upper and lower arm, said upper arms connected by a sliding contact support and said lower arms pressed by said collector washer against said sides to rotatably lock said spring wire to said drive head and a member between said flange and said upper arms having ribs transverse to said upper arms to engage said upper arms to form fulcrum points for resiliently pressing the sliding contact against the resistor.

11. In a rheostat having a base with a circular resistor engaged by a sliding contact and with a collectorring for receiving voltages from said contact, a drive means rotatably mounted on said base, the combination of a drive head having a lateral flange, a single piece of spring wire for supporting a sliding contact and a collector washer for slideably engaging the collector ring, said drive head secured to said drive means for rotation thereby, said spring wire having two S-shaped portions positioned on opposite sides of the drive head and generally longitudinal thereto each with an upper and lower arm, said upper arms connected by a sliding contact support and said lower arms pressed by said collector Washer against said sides to trotatab ly lock said spring Wire to said drive head, and said upper legs each having a raised portion for engaging the flange to form fulcrum points for resiliently pressing the sliding contact against the resistor.

12. A rheostat comprising a resistor with an engageahle conductive surface, electrical means extending 1ongitudinal to said surface for interchange of current with said engageable surface, a contact slideably engaging said surface, a collector member slideably engaging said electrical means, drive means extending lateral to said surface and said electrical means and having surfaces 1ongitudinal to said engageable surface, a resilient means positioned between said drive means surface and said electrical means, said resilient means formed from a single piece of spring Wire with two resilient portions on opposite sides of said drive means and extending longitu- References Cited in the file of this patent UNITED STATES PATENTS 1,987,118 Lodge Jan. 8, 1935 2,465,213 Dressel Mar. 22, 1949 2,594,493 Puerner Apr. 29, 1952 2,749,416 Steele June 5, 1956 2,790,882 Siegel Apr. 30, 1957 

1. A RHEOSTAT COMPRISING A BASE WITH A PERIPHERAL EDGE, A CIRCULAR FLANGE SPACED RADIALLY INWARD FROM THE PERIPHERAL EDGE TO FORM A SEATING SURFACE, A TERMINAL BLOCK EXTENDING FROM THE FLANGE TO THE PERIPHERAL EDGE; A RING TYPE RESISTOR EXTENDING OVER AN ARC OF LESS THAN 360* AND HAVING ENDS ADJACENT THE TERMINAL BLOCK; A COLLECTOR RING MOUNTED ON AND FASTENED TO SAID FLANGE FOR RECEIVING VOLTAGES TAPPED FROM SAID RESISTOR; DRIVE SHAFT ROTATABLY MOUNTED ON SAID BASE WITH A DRIVE HEAD HAVING A LATERAL FLANGE; A SINGLE PIECE RESILIENT MEMBER MOUNTED ON SAID DRIVE HEAD BETWEEN SAID LATERAL FLANGE AND SAID COLLECTOR RING TO SNUGLY PRESS SAID SHAFT ON SAID BASE AND SUPPORT A SLIDING CONTACT FOR ROTATION THROUGH THE ARC OF THE RESISTOR; SAID DRIVE SHAFT HAVING TWO KEYS ON OPPOSITE SIDES THEREOF WITH ONE KEY LONGER THAN THE OTHER; SAID DRIVE HEAD HAVING LONGITUDINALLY AND RADIALLY EXTENDING SLOTS FOR RECEIVING SAID KEYS; A METAL STOP MEMBER CONCENTRIC WITH THE SHAFT AND HAVING A LONGITUDINALLY EXTENDING STOP PROJECTION AND LATERAL PERIPHERAL PROJECTIONS; SAID FLANGE HAVING NOTCHES FACING SAID SHAFT AND SAID PROJECTIONS FITTING IN SAID NOTCHES TO PREVENT ROTATION OF SAID METAL STOP MEMBER; SAID LONGITUDINALLY EXTENDING PROJECTION OVERLAPPING WITH SAID LONG KEY TO FORM A STOP MEANS LIMITING THE ARC OF TRAVEL OF THE SLIDING CONTACT TO THE ARC OF THE RESISTOR. 